Anomalous behavior of thermal conductivity at high temperatures for molecular crystals composed of flexible molecules
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The temperature dependence of thermal conductivity ¿(¿) of selected molecular polycrystals consisting of flexible molecules was investigated within 20–260¿K. The materials were para-chloronitrobenzene, pentachloronitrobenzene and freons F-112 and F-113. The ¿(¿) of these crystals increased with temperature in the interval where processes of phonon–phonon scattering were dominant. The increase was observed both in the orientationally-ordered and -disordered phases and is typical of the thermally activated heat transfer by localized molecular excitations [M. A. Strzhemechny et al., Chem. Phys. Lett. 647 (2016) 55]. In a wide interval of temperatures, irrespective of the glass transition temperature, the ¿(¿) could be described by a sum of three components: ¿(¿)¿=¿¿/¿ + ¿ + ¿¿¿(¿). The term A/T accounts for phonon–phonon scattering processes and B accounts for diffuse phonon scattering. The third contribution is described by the Arrhenius equation, ¿¿¿(¿)¿=¿¿0 ¿¿¿(-¿/kB¿), where E is the activation energy and ¿0 is the pre-exponential factor characterizing intensity of the activation process. A comparative analysis of anomalous thermal conductivities of some other molecular crystals was carried out. It was found that ¿0 linearly depended on E and a similar relationship was evident for a series of quasicrystals.
CitationHorbat¿nko, Y. [et al.]. Anomalous behavior of thermal conductivity at high temperatures for molecular crystals composed of flexible molecules. "Journal of physics and chemistry of solids", 1 Abril 2019, vol. 127, p. 151-157.